1. Field of the Invention
The invention relates to a method for localizing a plurality of ground transmitters in a broadband context from the passing by of carrier without a priori knowledge on the signals sent. The carrier may be an aircraft, a helicopter, a ship, etc.
The method is implemented, for example iteratively, during the passing by of the carrier.
2. Description of the Prior Art
The prior art describes different methods to localize one or more transmitters from a passing carrier.
FIG. 1 illustrates an example of airborne localization. The transmitter 1 is in the position (x0,y0,z0) and the carrier 2 at the instant tk is at the position (xk,yk,zk) and perceives the transmitter at the incidence (θ(tk,x0,y0,z0),Δ(tk,x0,y0,z0)). The angles θ(t,x0,y0,z0) and Δ(t,x0,y0,z0) evolve in time and depend on the position of the transmitter as well as the trajectory of the carrier. The angles θ(t,x0,y0,z0) and Δ(t,x0,y0,z0) are identified as can be seen in FIG. 2 relative to a network 3 of N antennas capable of being fixed under the carrier.
There are many classes of techniques used to determine the position (xm,ym,zm) of the transmitters. These techniques differ especially in the parameters instantaneously estimated at the network of sensors. Thus, localising techniques can be classified under the following categories: use in direction-finding, use of the phase difference between two distant sensors, use of the measurement of the carrier frequency of the transmitter, use of the propagation times.
The patent application FR 03/13128 by the present applicant describes a method for localising one or more transmitters from a passing carrier where the direction vectors are measured in the same frequency channel and are therefore all at the same wavelength.
The method according to the invention is aimed especially at achieving a direct estimation of the positions (xm,ym,zm) of each of the transmitters from a blind identification of the direction vectors of the transmitters at various instants tk and various wavelengths λk.
Parametrical analysis will have the additional function of separating the different transmitters at each wavelength-instant pair (tk, λp(k)). The parameters of the vectors coming from the different pairs (tk, λp(k)) are then associated so that, finally, a localisation is performed on each of the transmitters.